Daily pattern of %VO2max and heart rates in normal and undernourished school children.

The pattern of usage of the VO2max, expressed as %VO2max during ordinary school days, with minute-by-minute heart rate recording, was studied in 106 boys and 83 girls, 6-16 yr of age divided into three age groups (6-8, 10-12, and 14-16 yr), living under economically deprived conditions in Colombia and classified as nutritionally normal or marginally malnourished. In a 12-h period, the 12 groups of children spent, on the average, 7-10 h at less than 30% VO2max, 1.5-4 h at 30-50% VO2max, and an accumulated time of 20-60 min above 50% VO2max. The latter occurred in short bursts rather than during sustained periods. There was a statistically significant but small decrease (approximately -3%) in the average 12 h %VO2max with age but no effects of sex or nutritional status. The overall average was about 25% VO2max in all groups. The data may suggest the existence of the regulation of physical activity to some level easily sustainable for long periods. Expressing the data as 30 min averages during 5 h of school and 5 h of free-time activity allows for the possibility of seeing group differences during shorter periods of time. This may prove useful in exercise training programs and studies of effort in the workplace.